1. Field of the Invention:
This invention relates to charge coupled devices and more particularly to forward scuppering to reduce noise and remove offsets among a plurality of charge coupled devices.
2. Description of the Prior Art:
A variety of methods have been developed for placing a predetermined amount of charge in the channel of a charge coupled device (CCD). One such method was described in U.S. Pat. No. 4,112,456 which issued on Sept. 5, 1978 to D. R. Lampe et al., and assigned to the assignee herein entitled "Stabilized Charge Injector for Charge Coupled Devices with Means for Increasing the Speed of Propagation of Charge Carriers". In U.S. Pat. No. 4,112,456, the channel was formed by a depletion region in N-type material with a plurality of electrodes over top, insulated by a layer of silicon dioxide for transferring the charge in the channel. A P+ region was formed at one end of the channel and at times was biased for injecting charge into a holding well in the channel and at other times biased for scuppering or removing charge from the holding well over a predetermined potential barrier within the channel. A precise amount of charge was therefore placed in the holding well as a function of the potential barrier between the holding well and the P+ region. The scuppering action removed the charge at the end of the channel. It does not show or suggest, however, using the semiconductor material on the other side of the P+ region as part of the channel. The scuppering action removed the charge from a holding well in the opposite direction to the transfer of the remaining charge.
Also in the prior art, the fabrication of vertical PNP transistors is well known, comprising an emitter region at the surface, a base region having a predetermined width below the surface and a collector region, substrate, below the base region.
It is therefore desirable to provide charge equalization in a holding well of a charge coupled device where a portion of the charge is scuppered forward of the holding well rather than in the reverse direction as in most scuppering techniques.
It is further desirable that the structure within the charge coupled device that permits scuppering of charge forward of the holding well also permits charge to be transported past this portion of the charge coupled device in the channel.
It is further desirable to fabricate a vertical PNP transistor within the channel of a charge coupled device which exhibits bipolar action when the emitter junction is forward biased to remove charge in the channel and which exhibits no bipolar action at times the emitter is reverse-biased.
It is further desirable to provide a means utilizing a bipolar transistor structure incorporating the channel of a CCD device to couple minority charge from the channel and to convert the minority charge to majority charge in a conductor to provide a signal in the form of current or potential.